Method of producing copper clad steel



United States Patent Thomas T. Watson, Coatesville, Pa., assignor toLukens Steel Company, Coatesville, Pa., a corporation of Pennsylvania N0Drawing. Application May 7, 1951, Serial No. 225,066

6 Claims. (Cl. 29-4709) The present invention relates to the manufactureof copper clad steel plates; and more particularly it relates to amethod for making copper clad steel plates from large masses of themetals, that is, from steel slabs or ingots, as distinguished from steelplates or sheets, and from copper plates as distinguished from coppersheeting or foil.

The manufacture of copper clad steel sheets, and of articles therefrom,such as cooking utensils, is well known. Such sheet ware is normallyprepared by pressing together at high temperatures, a copper sheet orfoil and a steel sheet to cause the welditn of the copper sheet or foilto the steel sheet. Cooking utensils can readily be fabricated from suchsheet ware. It has also been suggested to clad the copper sheet or foilto the steel sheet by a hot rolling operation, whereby in addition towelding of the copper to the steel, some slight reduction in thicknessof the composite article may take place. While the cladding of coppersheets or foils to steel sheets by such procedures presents problems,they are relatively minor in view of the thinness of the stock beingworked.

The manufacture of copper clad steel plates from large masses of themetals, that is from copper plates and from steel slabs or ingots,however, is an entirely different matter. Aside from the large size ofthe material being worked which gives rise to handling problems anddifiiculties during hot rolling, the large mass of metals being workedgives rise to other difiiculties which, heretofore, have made itimpossible to obtain satisfactory bonding between the copper and thesteel.

bond resulting in a defective product. Possible reasons for this will beset forth hereinafter. At any rate it has been found that by usingcopper plates made from a special type of copper, this formation ofblisters is eliminated. In the second place, it was found that, inattempting to manufacture copper clad steel plates from large masses ofcopper and steel of the stated type, by a hot rolling procedure, thestrength of the bond between the copper and the steel was very much lessthan that of even the copper itself. While this is believed to be dueprimarily to the difficulty of forming a copper-steel alloy at the bondinterface, it is also believed to be aggravated by the tremendousstrains set up during hot rolling due to the widely differing physicalproperties between the copper and the steel at the rolling temperatures.(The normal hot rolling temperature for carbon steel is 2300-2400 F.Yet, ordinary copper melts at several hundred degrees below this range,and is a relatively soft metal even at ordinary temperatures. Thus, attemperatures suitable for rolling copper, the steel is very much lessductile, and with standard rolling procedure for steel the copper tendsto take up most of the strain from the rolls causing it to be squeezedout beyond the edges of the steel.)

Moreover, in hot-rolling during cladding of large masses of metal theonly practical way initially to se- In the first place, it was foundduring early work, that blisters formed at the 2,707,323 Patented May 3,1955 cure the copper plate to the steel slab or ingot, or to secure aplurality of such composite assemblies into a sandwich or pack, is bywelding around the peripheral edge of the assembly or pack. However, dueto the wide differences in deformation characteristics between thecopper and the steel at rolling temperatures, the copper, under normalrolling techniques, would, as'stated, be caused to be squeezed beyondthe edge of the assembly rupturing the initial weld. In addition, whileweld metal is sufiiciently ductile at normal steel rolling temperatures,i. e., at 23002400 F., to withstand the strains of rolling withoutbreaking, it tends to rupture, under normal hot rolling technique, atthe temperatures usable for copper cladding of steel, thereby renderingthe assembly unfit for further rolling.

The foregoing are a few of the many problems encountered in attempts toproduce copper clad steel plates from large masses of the metals, andhave been cited to show that such manufacture represents a fieldentirely different from that where copper clad steel sheets, or otherclad steel sheets, are prepared from thin metal stock such as sheets orfoils, by pressing or hot rolling involving but slight reduction inthickness.

It is an object of the present invention to provide a method for themanufacture, by hot rolling, of copper clad steel plates from largemasses of the metals, that is, from copper plates and steel slabs oringots.

Another object is to provide a process of the type described whereby, inthe product formed, the strength of the bond between the copper and thesteel is equal to or greater than the strength of the copper itself.

Still another object is to provide a process of the type describedwhereby, in the product formed, the bond between the copper and steel isfree from blisters or other defects.

A further object of the invention is to provide a process of the typedescribed wherein the danger of rupturing the initial sealing weldsduring rolling is eliminated.

A further object is to provide a process of the type described wherein aplurality of copper clad steel plates may be produced during oneoperation.

Other objects will be apparent from a consideration of the followingspecification and claims.

In accordance with the present invention a series of novel steps andfeatures, each dependent on the other, are combined in a novelcorrelated manner to provide a process by which the above-stated objectsmay be realized. The process comprises electrodepositing a layer ofnickel on a face of a plate of oxygen-free copper; securing the copperplate to a steel slab or ingot with the nickel-plated surface of thecopper plate in face-to-face contact with the steel slab or ingot;heating the resulting composite assembly uniformly throughout to atemperature between about 1550 and about 1800 F; and subjecting the hotassembly to pressure rolls to reduce its thickness to between aboutonefourth and about onetwenty-fifth of the thickness of the originalassembly, the reduction in thickness of said copper-steel assemblyduring any one pass through the rolls being no greater than aboutone-eighth of an inch. In accordance with the preferred embodiment ofthe process, the reduction in thickness of the copper-steel assembly perpass during the first series of passes is no greater than aboutone-eighth of an inch, as stated. Then, when the copper-steel assemblyis within 10% of the desired final thickness, the reduction in thicknessof the copper-steel assembly per pass is no greater than aboutone-sixteenth of an inch.

By the above-described process it has been found that the difficultieswhich previously rendered the manufacture of satisfactory copper cladsteel plates from large masses of the metals impossible, are eliminated,and that consistently excellent copper clad steel plate products are'ice -29 obtained. By the use of oxygen-free copper it has been foundthat the blisters, which form when ordinary copper is used, are notencountered. It is believed that the freedom of the copper fromdissolved oxygen is directly responsible for this. Ordinary coppercontains about 0.04%' oxygen. When ordinary copper is used, it isbelieved that, at the high temperatures to which the large mass of metalmust be subjected in order to heat it throughout to the rollingtemperature, a gas, which may be oxygen, carbon dioxide or steam, ormixtures thereof, forms at the bond line. Carbon dioxide may form byreaction of the oxygen with carbon in the copper or steel, or withcarbon monoxide in the reducing atmosphere of the soaking pit; and steammay form by reaction between the oxygen and hydrogen from the furnaceatmosphere or liberated from the steel during heating. At any rate theformation of the gas results in blisters at the bond providing adefective product. As stated, when oxygenfree copper plates are usedthere is no formation of blisters. provided between the copper and thesteel is very strong, and, in fact, shear tests have shown that thestrength of the bond is even greater than that of the copper itself. Theuse of oxygen-free copper in conjunction with the electrodeposition ofnickel on the copper plate is bedure recited, where the maximumreduction in thickness per pass is only one-half to one-third of thatconventionally employed in hot rolling during cladding of steel withother metals. In addition to this, it has been found that by theparticular rolling procedure recited, even reduction in thickness of thesteel as well as the copper J takes place, and there is no extrusion ofthe copper be yond the edge of the steel, which would break the initialsecuring weld and otherwise disrupt the rolling procedure. Moreover, ithas been found that by such a rolling procedure, even at relatively lowtemperatures employed as compared to conventional cladding operations,the initial sealing weld is not ruptured in spite of its low ductility.

Referring to the copper used as the starting material in accordance withthe present process it is, as stated.

oxygen-free copper in the form of a plate, that is, it will have athickness of at least one-eighth inch and it may have a thickness up toabout one inch. Oxygen-free copper, as it is known in the art, is copperprepared under conditions preventing the retention of the normal amountof oxygen therein. For example, such copper may be obtained byelectrodeposition followed by melting, as in an electric furnace, underan inert atmosphere such as nitrogen. During pouring, the molten copperis also protected from the atmosphere. Such copper may also be obtainedby treating copper, during conventional manufacturing procedures, forthe removal of oxygen with an agent, such as phosphorus, manganese, andthe like. Such copper is also known in the art as deoxidized copper. Thecopper prepared by any of the procedures described above issubstantially free of oxygen but may contain minute traces thereof. Suchcopper is referred to herein and in the claims as oxygen-free copper,and such term is used herein in the sense it is used in the art to referto a copper containing no more than a trace of oxygen and to distinguishfrom ordinary copper which contains about 0.04% oxygen. While anyoxygen-free copper may be employed in accordance with, the presentprocess, the preferred form is the de-oxidized.

By the present process, moreover, the bond 4 copper; referred to above,particularly phosphorus deoxidized copper.

The steel body which is employed in accordance with the present processfor cladding with copper is, as stated, in the form of a slab or ingot.An ingot is the form of the steel as it comes from the ingot mold, whilea slab is prepared by rolling the rough ingot, to reduce it somewhat inthickness and to provide a smoother surface. The steel body, whetherslab or ingot, employed in the present process will be at least twoinches in thickness, and the thickness thereof may run up to aboutfifteen inches. With respect to the steel itself it may be any carbonsteel or low alloy steel, that is, a steel containing less than about 6%of alloying materials. Such low alloy steels are steels in whichrelatively small amounts of other metals (such as nickel, titanium,chromium, molybdenum, manganese, and the like, and various combinationsthereof, such as nickel and titanium; nickel and chromium; nickel,chromium and molybdenum; and the like), are incorporated in the steel toenhance the physical properties thereof, mainly tensile strength, asdistinguished from chemical properties such as corrosion resistance.

The surface of the steel slab or ingot to which the copper is to be cladis preferably substantially free of oxide scale. Thus, one face of thesteel slab or ingot may be, and preferably is, treated to remove oxidescale as by grit blasting, pickling, and the like, before the copperplate is secured thereto. Grit blasting is particularly advantageous inthis regard.

The surface of the copper plate which is to be clad to the steel isprovided, as stated, with a layer of electrodeposited nickel. In orderto obtain satisfactory plating of the copper by the nickel it isdesirable that the surface of the copper plate be clean and free fromoxide. Thus, it is desirable to clean the surface of the copper plate bypickling, such as in a hydrochloric acid bath. Before pickling, thesurface may be preliminarily cleaned in an electrolytic caustic bathcontaining, for example, an aqueous solution of caustic soda, or ofcaustic soda and sodium carbonate, after which the plate may be washedwith water. Imperfections in the surface of the copper plate may beremoved by bufiing.

The provision of the nickel coating is conveniently accomplished byimmersing the copper plate, after cleaning in the manner stated, in anickel electroplating bath to provide an electrolytic deposit or coatingof nickel on the surface of the plate. To prevent nickel from beingplated on both surfaces of the plate, one side may be coated with astrippable film-forming material which prevents plating of the nickel onthe surface to which it is applied, and, after plating, this film can bereadily stripped from the unplated surface. While this coating may beprovided by any strippable, film-forming material which is relativelyunaffected by acids or bases, the use of a liquid composition whichdries to a nonadhesive film and which is compounded from modified halidepolymers, condensation resins and diene derivatives (known as TygonTemprotec, which is a registered trade-mark) is particularlyadvantageous. The electroplating bath will comprise a soluble nickelsalt, such as nickel chloride, nickel sulfate, and the like, and astrong mineral acid such as hydrochloric acid, sulfuric acid, and thelike, and a nickel anode or anodes may be provided. The electroplatingof nickel on copper is in itself well known, and thus the provision ofthe nickel coating on the surface of the copper plate will present noproblem to one skilled in the art. Insofar as the present process isconcerned, however, the electroplating procedure will be controlled toprovide a nickel coating having a thickness between about 0.001 andabout 0.020, a coating having a thickness between about 0.002 and about0.005" being preferred.

After the nickel coating has been deposited on the surface of the copperplate, and after the strippable film,

if used, has been removed from the other surface of the copper plate,the nickel-plated copper plate is positioned with respect to the steelslab or ingot so that the nickel coating is in face-to-face contact withthe steel body. The copper plate will have a length and width somewhatsmaller than that of the steel body to provide a margin of from about 1inch to about 4 inches between edges of the copper plate and the edgesof the steel body.

The copper plate and the steel body are then firmly secured together inthe stated position. When the entire assembly to be rolled for claddingis to consist of one copper plate and one steel slab or ingot, a steelplate or slab may be placed over the copper plate and secured to thesteel slab or ingot, thus holding the copper plate firmly against thebase steel slab or ingot. The steel cover plate or slab may be securedto the steel slab or ingot by welding at the marginal edges; oradvantageously steel spacer bars are placed in the gap between the coverplate or slab and base steel slab or ingot and these in turn are weldedto the cover plate or slab and to the base steel slab or ingot toprovide a compact unitary article. A weld-preventing material may beincorporated between the steel cover plate or slab and the copper plateto prevent welding thereof together during hot rolling. In accordancewith the preferred embodiment of the invention, a plurality of copperplate-steel slab or ingot assemblies are secured into a single pack sothat more than one copper clad steel plate may be produced in a rollingoperation. For example, two copper plates may be sandwiched between twosteel slabs or ingots, the nickel-coated face of each copper plate beingin face-to-face relationship with the respective steel body to which itis to be clad. A weldpreventing material may be provided between thecopper plates to prevent welding thereof together. The resultingsandwich or pack may be rigidly secured into a unitary structure bywelding around the marginal edges, steel spacer bars advantageouslybeing provided in the marginal gap between the steel bodies in themanner stated above.

Reference has been made above to a weld-preventing composition toprevent welding, during hot rolling, of the copper plate to the steelcover plate or to the adjacent copper plate in the event a plurality ofcopper plate-steel slab or ingot assemblies are assembled into a pack orsandwich. While any weld-preventing composition may be employed for thispurpose, a particularly advantageous weld-preventing composition is thatdisclosed and claimed in co-pending application Serial Number 130,598filed December 1, 1949, by Thomas T. Watson and Albert Riggall. Theweld-preventing composition of this stated co-pending applicationcomprises a finely-divided refractory inorganic material in a liquidvehicle comprising a very small amount of cellulose ether or esterdissolved in a volatile solvent.

The composite assembly or pack secured into a unitary structure asdescribed above is then heated uniformly throughout to the rollingtemperature. Heating prefe.- ably takes place in a soaking pit where theassembly can be subjected to high temperatures for extended periods. Thetemperature to which the assembly is heated will not exceed about 1800F., and may be as low as about 1550 F. However, it is preferred to heatthe assembly to a temperature between about 1600 F. and about 1725 F.

The hot assembly is then subjected to pressure rolls to provide pressurefor welding the copper plate to the steel slab or ingot and to reducethe composite article to the desired thickness. As stated above, theamount of reduction in thickness of the assembly per pass is critical,and must not exceed about one-eighth inch for each copper plate-steelslab or ingot assembly. Thus, where two copper plate-steel slab or ingotassemblies are rolled in the form of a pack or sandwich in accordancewith the preferred embodiment of the present invention, the reduction inthickness per pass of the pack should not exceed about one-fourth inch.This is a marked departure from normal hot rolling procedures forcladding where the amount of reduction in thickness per pass is morethan two to three times this amount. Rolling is continued in the mannerstated until the desired reduction in thickness is obtained, which, asstated, will normally be where the assembly or pack is between aboutone-fourth and about one-twenty-fifth its original thickness, preferablybetween about one-sixth and about one-twelfth of its original thickness.This will provide, in view of the size of the starting materials, copperclad steel plate.

In accordance with the preferred form of the process, when the assemblyor pack has been reduced in thickness to within about 10% of the desiredfinal thickness, the reduction in thickness per pass for eachcopper-steel assembly will not exceed about one-sixteenth of an inch.This procedure insures the advantageous results obtained in accordancewith the present process.

Following rolling, the product may be treated as desired. Rough edgesmay be cut evenly and initial weld metal sheared away. When a pluralityof assemblies has been rolled in the form of a pack, the resultingcopperclad steel plates can be readily separated from each other byshearing around the edges to remove weld metal.

The operation of the present process will be more readily understoodfrom a consideration of the following specific example which is givenfor the purpose of illustration and is not intended to limit the scopeof the invention in any way.

Example In this example two copper plates and two steel slabs are rolledtogether in the form of a pack to produce simultaneously two copper cladsteel plates. The copper plates are of phosphorus deoxidized copper and74" long, 48 wide and thick. The steel slabs are carbon steel slabs 78%"long, 52%" wide and 3%" thick.

Steel lugs are first welded to one edge of each copper plate tofacilitate handling. The plates are then pickled in hydrochloric acidand rinsed with water, and imperfections on the surfaces of the platesare removed by bufiing. To one face of each of the plates is applied astrippable organic film. The plates are then electrically cleaned in acaustic tank, sprayed with water to remove traces of the causticsolution, and then pickled in hydrochloric acid and rinsed with water.

The thus-cleaned plates are then immersed in a Watts bath for nickelplating. A current density of 50 amperes per square foot is employed toprovide a nickel coating 0.003 thick on the face of each copper platewhich is not protected by the organic film.

Following plating the copper plates are rinsed with water, and thestrippable organic film and handling lugs are removed. A weld-preventingcomposition is applied to each of the non-plated faces.

One face of each of the steel slabs is grit blasted to remove oxidescale. The two copper plates are then sandwiched between the two steelslabs so that the weldpreventing composition is between the copperplates and so that the nickel-coated face of each copper plate is inface-to-face contact with a grit-blasted face of the steel slab to whichit is to be clad. The smaller copper plates are centered on the steelslabs to provide a margin between the edges of the plates and the edgesof the steel slabs. Steel bars are then laid in the gap between thesteel slabs, and the bars and the slabs are welded together to securethe metal members into a unitary pack.

The pack is then placed in a soaking pit where it is held until heateduniformly throughout to 1700 F. The pack is then transferred to arolling mill where it is repeatedly passed between the rolls until it isreduced to a thickness of one inch. The rolling mill is adjusted so thatthe reduction in thickness of the pack per pass through the rolls duringthe first series of passes is about 7 Then when the pack is reduced inthickness to about 1%", the rolls are adjusted so that the reduction inthickness per pass is about 1 and two passes are made at thisadjustment. Then the reduction in thickness is gradually reduced furtheruntil the final one inch thickness is reached.

After rolling, the weld metal at the edges of the cornposite product issheared away leaving two 10% copper clad steel plates 240 inches long,80 inches wide and /2 inch thick.

The shear strength of the resulting plate at the bond is 25,00027,000 p.s. i. when tested by the standard A. S. M. E. shear test, whereas theshear strength of the deoxidized copper itself is 22,000 p. s. i. Copperclad steel plates made following the same procedure but with out nickelplating the copper plates had a shear strength at the bond of onlyl7,00.0-l9,000 p. s. i.

Considerable modification is possible in the selection of the particulartechniques to be followed in carrying out the process of the presentinvention without departing from the scope thereof.

I claim:

1. The method of manufacturing copper-clad steel plates that includesthe bonding of one face of an oxygenfree copper plate and a steel slabor ingot wherein the former varies from Vs" to 1" in thickness as thelatter varies from 2" to in thickness, which method compriseselectrodepositing a layer of nickel on one face of said copper plate;securing the copper plate to. a steel slab or ingot with thenickel-plated surface of the copper plate in face-to-face contact withthe steel slab or ingot; heating the resulting composite assemblyuniformly throughout to a temperature between about 1550 and about 1800"F; and subjecting the hot assembly to pressure rolls to reduce itsthickness to between about onefourth and about one-twenty-fifth of thethickness of the original assembly, the reduction in thickness of saidcopper-steel assembly per pass through the rolls being no greater thanabout one-eighth of an inch, and, when the thickness of the assembly iswithin about 10% of the desired final thickness, the reduction inthickness of said copper-steel assembly per pass through the rolls beingno greater than about one-sixteenth of an inch.

2. The method of claim 1 wherein the assembly is heated uniformly to atemperature between about 1600 F. and about 1725 F. and wherein theassembly is rolled until its thickness is reduced to between aboutone-sixth and about one-twelfth of its original thickness.

3. The method of manufacturing copper-clad steel plates thatincludes thebonding of the faces of oxygenfree copper plates and steel slabs oringots wherein the former vary from /s" to. 1" in thickness as thelatter varies from 2" to 15" in thickness, which method compriseselectrodepositing a layer of nickel on one of the faces of each of twocopper plates; securing the nickelplated copper plates between two steelslabs or ingots, the nickel-plated face of each copper plate being infaceto-face contact with a steel slab or ingot to form a unitary pack;applying a weld-preventing material between the juxtaposed faces of thecopper plates; heating thepack uniformly throughout to a temperaturebetween about 1550 F. and about 1800 F.; and subjecting said pack topressure rolls to reduce its thickness to between about one-fourth andabout one-twenty-fifth of the thickness of the original pack, thereduction in thickness of said pack per pass through the rolls being nogreater than about one-fourth of an inch.

4. The method of claim 3 wherein said pack is heated uniformlythroughout to a temperature between about 1600 F. and about 1725 F.

5. The method of manufacturing copper-clad steel plates that includesthe bonding of the faces of oxygenfree copper plates and steel slabs oringots wherein the former vary from A3 to 1 in thickness as the lattervaries from 2" to 15" in thickness, which method compriseselectrodepositing a layer of nickel on one of the faces of each of twocopper plates; securing the nickelplated copper plates between two steelslabs or ingots, the nickel-plated face of each copper plate being inface-toface contact with a steel slab or ingot to form a unitary pack;applying a weld-preventing material between the juxtaposed faces of thecopper plates; heating the pack uniformly throughout to a temperaturebetween about 1550 F. and about 1800 F.; and subjecting said pack topressure rolls to reduce its thickness to between about one-fourth andabout one-twenty-fifth of the thickness of the original pack, thereductionin thickness of said pack per pass through the rolls being nogreater than about one-fourth of an inch, and, when the thickness of theassembly is within about 10% of the desired final thickness, thereduction in thickness of said pack per pass through the rolls being nogreater than about one-eighth of an inch.

6. The method of claim 5 wherein said pack is heated uniformly to atemperature between about 1600 F. and about 1725" F. and wherein thepack is rolled until its thickness is reduced to between about one-sixthand about one-twelfth of its original thickness.

References Cited in the file of this patent UNITED STATES PATENTS959,517 Grifllth May 31, 1910 1,956,818 Acre May 1, 1934 2,020,477 ScottNov. 12, 1935 2,053,096 McKay Sept. 1, 1936 2,115,750 Rubin May 3, 19382,174,733 Chace Oct. 3, 1939 2,269,523 Deutsc'h Jan. 13, 1942 2,325,659Chace Aug. 3, 1943 2,366,178 Chace Jan. 2, 1945 2,468,206 Keene Apr. 26,1949 2,473,712 Kinney June 21, 1949 2,474,038 Davignon June 21, 1949

1. THE METHOD OF MANUFACTURING COOP-CLAD STEEL PLATES THAT INCLUDES THEBONDING OF ONE FACE OF AN OXYGENFREE COOPER PLATE AND A STEEL SLAB ORINGOT WHEREIN THE FORMER VARIES FROM 1/8" TO 1" IN THICKNESS AS THELATTER VARIES FROM 2" TO 15" IN THICKNESS, WHICH METHOD COMPRISESELECTRODEPOSITING A LAYER OF NICKEL ON ONE FACE OF SAID COOPER PLATE;SECURING THE COPPER PLATE TO A STEEL SLAB OR INGOT WITH THE NICKEL-PLATESURFAE OF THE COPPER PLATE IN FACE-TO FACE CONTACT WITH THE STEEL SLABOR INGOT; HEATING THE RESULTING COMPOSITE ASSEMBLY UNIFORMLY THROUGOUTTO A TEMPERATURE BETWEEN ABOUT 1550 AND ABOUT 1800* F., AND SUBJECTINGTHE HOT ASSEMBLY TO PRESSURE ROLLS TO REDUCE ITS THICKNESS TO BETWEENABOUT ONEFOURTH AND ABOUT ONE-TWENTY-FIFTH OF THE THICKNESS OF THEORIGINAL ASSEMBLY, THE REDUCTION IN THICKNESS OF SAID COPPER-STEELASSEMBLY PER PASS THROUGH THE ROLLS BEING NO GREATER THAN ABOUTONE-EIGHT OF AN INCH, AND, WHEN THE THICKNESS OF THE ASSEMBLY IS WITHINABOUT 10% OF THE DESIRED FINAL THICKNESS, THE REDUCTION IN THICKNESS OFSAID COPPER-STEEL ASSEMBLY PER PASS THROUGH THE ROLLS BEING NO GREATERTHAN ABOUT ONE-SIXTEENTH OF AN INCH.